JPH10294120A - Operating method for phosphoric acid fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize operation by properly obtaining the refilling time of phosphoric acid kept in cells that constitute a fuel cell layered product. SOLUTION: A fuel cell layered product 10 is constructed by laminating unit blocks 20, which are built by laminating multiple cells 11 interposing separators 12 between them, interposing cooling plates 13 between them. In this case, an output current, an output voltage and a temperature of a cell- cooling water supplied to the cooling plates are measured with an ammeter 16, a voltmeter 15 and a thermometer 17, respectively; from these values the maximum temperature of the cells 11 is calculated and also the phosphoric acid scattering amount is obtained by measuring its scattering velocity; when these values have reached an upper limit, the phosphoric acid is refilled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phosphoric acid fuel cell using phosphoric acid as an electrolyte, and relates to an operation method for recognizing and replenishing the amount of electrolyte which is reduced by evaporation and scattering.

[0002]

2. Description of the Related Art FIG. 3 is a sectional view schematically showing the structure of a unit cell which is a basic structural unit of a fuel cell stack of a phosphoric acid type fuel cell. The unit cell has a configuration in which a fuel electrode 6 and an air electrode 7 are arranged on both surfaces of a matrix 1 holding phosphoric acid, and a reservoir plate 9 holding phosphoric acid is arranged outside the fuel electrode 6 and the air electrode 7. The fuel electrode 6 is composed of the fuel electrode catalyst layer 2 and the fuel electrode substrate 4 provided with a gas flow path 8 for allowing fuel gas to flow. The air electrode is formed of the air electrode catalyst layer 3 and air. The air electrode substrate 5 is provided with a gas flow path 8 for flowing.

FIG. 4 is a cross-sectional view showing the structure of a main part of a fuel cell stack constructed using the unit cells having the above-described structure. A unit cell 11 is sequentially stacked via a separator 12 to form a block, and the block is stacked with a cooling plate 13 interposed therebetween to form a fuel cell stack. A gas supply / discharge manifold is installed on each side of the fuel cell stack, and a fuel gas having a high hydrogen concentration is supplied to the gas flow path 8 of the fuel electrode of each unit cell, and air or the like is supplied to the gas flow path 8 of the air electrode. Is supplied to the fuel electrode catalyst layer 2 and the air electrode catalyst layer 3 to obtain electric energy by an electrochemical reaction. Further, since this electrochemical reaction is an exothermic reaction, the generated heat is removed by supplying the cell cooling water to the cooling plate 13 interposed in the fuel cell stack, and the unit cell 11 is brought to a predetermined operating temperature. keeping.

[0004] In this configuration, the phosphoric acid retained in the matrix evaporates as the temperature rises and gradually disperses with the flow of the supplied fuel gas or oxidizing gas.
Retention decreases gradually. When the amount of retained phosphoric acid decreases in this manner, the gas sealing performance of the fuel gas and the oxidizing gas by the matrix decreases, and these gases directly react with each other, causing damage to the fuel cell stack. For this reason, in the conventional phosphoric acid type fuel cell, as shown in FIG. 4, voltage measurement leads 14A and 14B are provided on the cooling plate 13 and the output voltage of the block is measured by the voltmeter 15, and the abnormal voltage is detected. The occurrence of a shortage of phosphoric acid is detected by the decrease, and the matrix is replenished with phosphoric acid based on this abnormal signal, so that a predetermined amount of phosphoric acid is constantly held.

[0005]

In the conventional phosphoric acid fuel cell, as described above, the power generation voltage of each block in which the unit cells are stacked is measured, and the shortage of phosphoric acid is detected by detecting the abnormal decrease. The scattering speed of the phosphoric acid depends on the flow rates of the fuel gas and the oxidizing gas, and also varies depending on the temperature of the battery as shown in FIG. The flying speed also increases. On the other hand, since each block is cooled by the cooling plates located at both ends and maintained at a predetermined temperature, in each block, the temperature of the unit cell adjacent to the cooling plate is the lowest, and the temperature of the unit cell located in the central portion is Is the highest. Therefore, the scattering rate of phosphoric acid in each unit cell constituting the block will be different, and when the measured power generation voltage of the block begins to decrease abnormally, the fuel gas and the oxidized gas in the unit cell with the largest scattering amount have already been observed. In many cases, irreparable damage has progressed due to direct reaction with the agent gas, and there has been a problem that it is not always appropriate as a method for detecting the time of replenishing phosphoric acid.

An object of the present invention is to provide a method of operating a phosphoric acid type fuel cell which can accurately detect the time of replenishment of phosphoric acid held in a unit cell constituting a fuel cell stack and can operate stably. It is in.

[0007]

In order to achieve the above-mentioned object, in the present invention, a unit cell formed by arranging a fuel electrode and an air electrode on both surfaces of a matrix holding phosphoric acid as an electrolyte is provided. A cooling plate provided with a cooling pipe is appropriately inserted and laminated, a battery cooling water is passed through the cooling pipe, a fuel gas is supplied to a fuel electrode, and an oxidant gas is supplied to an air electrode. (1) Output current and power generation time, or output voltage and / or battery cooling water, output current and power generation time are measured. The replenishment time is calculated, and the operation is performed by replenishing the electrolyte.

(2) Alternatively, the amount of generated power and the generation time,
Alternatively, the amount of generated power, the generated time, and the battery cooling water temperature are measured, and the time for replenishing the electrolyte is calculated from these measured values.
It is assumed that the fuel cell is operated by replenishing the electrolyte. As shown in FIG. 4, the fuel is constituted by a block in which a plurality of unit cells 11 are stacked with a separator 12 interposed therebetween and a cooling plate 13 provided with cooling pipes at both ends is provided as a unit. In the battery stack, the maximum temperature of the unit cell 11 inside each block is determined by the amount of heat generated in the block, the heat diffusion condition, and the cooling condition of the cooling plate 13. Of these, the amount of heat generated in the block is determined by the output current and the output voltage, and the heat diffusion conditions in the block are determined by the unit cell 11 and the separator 12.
Heat transfer performance, that is, heat resistance. The cooling condition of the cooling plate 13 is determined by the temperature condition of the battery cooling water flowing through the provided cooling pipe and the heat transfer performance of the cooling plate 13, that is, the thermal resistance. Among these factors, the thermal resistance of the unit cell 11 and the separator 12 and the cooling plate 1
The thermal resistance of No. 3 is specific to the configuration and is constant. Therefore, if the output current and the output voltage and the temperature condition of the battery cooling water are known, the maximum temperature to which the unit cell 11 is exposed is known.

On the other hand, as shown in FIG. 5, the scattering speed of the phosphoric acid in the electrolyte held in the matrix depends on the held temperature, and increases as the temperature increases. Unit cell 1 exposed to
In No. 1, phosphoric acid is scattered most rapidly. Therefore, as described in (1) above, if the output current, output voltage and battery cooling water temperature are known, the maximum scattering speed of phosphoric acid in the above-described block is known, and the power generation time is measured to deviate from the maximum scattering speed. For example, the maximum amount of scattering is known, and if the replenishment time is set based on this value, replenishment can be performed without causing a shortage of phosphoric acid. In the above description, the output voltage is the I-
It is also possible to obtain from the output current based on the V characteristic,
Also, since the battery cooling water temperature is usually used while being kept constant, it can be treated as a constant. Therefore, only the output current, or the output current and the battery cooling water temperature, or the output current and the output voltage, the maximum temperature, and thus the maximum scattering speed of phosphoric acid, is known, and the maximum scattering amount is measured using the measured value of the power generation time. It is known that the replenishment time of phosphoric acid can be appropriately set.

If the amount of generated power and the generation time are measured, the average generated power is known by dividing the generated power by the generation time. Furthermore, if an IV characteristic unique to the fuel cell stack is used, an average generated current can be obtained from the average generated power. Therefore, the generated power amount is used instead of the measured value of the generated current, and the generated power amount and power generation time or the generated power amount, power generation time and battery cooling water temperature are measured as described in (2) above. In this case, the maximum scattering amount of the phosphoric acid retained as the electrolyte is known, and the time for replenishing the phosphoric acid can be set appropriately.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION

<Embodiment 1> FIG. 1 is a cross-sectional view of a fuel cell stack operated according to Embodiment 1 of the method for operating a fuel cell of the present invention. The fuel cell stack 10 shown in the figure has a unit block 2 formed by stacking a plurality of unit cells 11 with a separator 12 interposed therebetween.
0, and the unit blocks 20 are further laminated with the cooling plate 13 interposed therebetween. Ammeter 1
6 is an ammeter for measuring the output current of the fuel cell stack 10, a voltmeter 15 is a voltmeter for measuring the voltage generated in the unit block 20, and the thermometer 17 is for the cooling plate 1
3 is a thermometer for measuring the temperature of the battery cooling water supplied to the cooling pipe incorporated in 3.

In the operation method of this embodiment, the unit is calculated from the output current measured by the ammeter 16, the output voltage measured by the voltmeter 15, and the temperature of the battery cooling water measured by the thermometer 17. The amount of the phosphoric acid scattered in the matrix of the cell 11 is calculated to determine the replenishment time of the phosphoric acid, and the fuel cell is operated using a method of replenishing the phosphoric acid based on the calculated timing.

That is, the output current is I [A], the generated voltage per unit cell is V [V], and the temperature of the battery cooling water is T _W
[° C.], the maximum temperature T _MAX [° C.] of the unit cell is expressed by the following equation.

[0014]

T _MAX = g (R _C , R _COOL , n) (1.26−V) I + T _W (1) where R _C is the thermal resistance of the unit cell, and R _COOL is the heat of the cooling plate. The resistance n is the number of unit cells stacked in each unit block, and g is a constant determined from these values. Therefore, by measuring the output current I, the generated voltage V, and the battery cooling water temperature T _W , the maximum temperature T _{MAX of the} unit cell is known from the equation (1).

On the other hand, the flow rates of air and fuel gas supplied to the air electrode and fuel electrode of each unit cell are F _A and F _F [mol / h], respectively, and the vapor pressure of the electrolyte at the temperature T [° C.] v (T) [atm], the molecular weight of the electrolyte is M
Then, the scattering speed w of the electrolyte at the temperature T [° C.]
(T) [g / h]

[0016]

W (T) = (F _A + F _F ) · M · v (T) (2) Among F _A, F _F is an oxygen utilization rate U
Assuming that O ₂ , the hydrogen utilization rate is UH ₂ , and the inlet hydrogen partial pressure is PH ₂ , it is expressed as a function of the output current I as in the following equations (3) and (4).

[0017]

F _A = I × 3600 / (4 × 96490 × 0.208 × UO ₂ ) (3) F _F = I × 3600 / (2 × 96490 × UH ₂ × PH ₂ ) (4) Therefore, every Δt output current I, generated voltage V, to measure the battery coolant temperature T _W, to calculate the maximum temperature T _MAX of the unit cell using the equation (1), then the vapor pressure of the electrolyte in the calculated T _MAX v (T _MAX ) and equations (3), (4)
Using the obtained gas flow rate, the temperature T
Calculating a flying rate w of the electrolyte in the _MAX (T _{MA X).} Further, by multiplying the obtained scattering velocity w (T _MAX ) by Δt, the amount of the electrolyte scattered in this time interval is calculated.
The measurement is repeated every Δt minutes to calculate the scattered electrolytic mass, and the sum is calculated to obtain the cumulative value of the scattered amount. When this value exceeds the upper limit of the scattered amount as shown in FIG. Replenish.

In the above description, the output current I, the generated voltage V, and the battery cooling water temperature T _W are measured every Δt, but the IV characteristic of the unit cell, V = f (I), is used. For example, the maximum temperature T _MAX of the unit cell is expressed by the following equation.

[0019]

T _MAX = g (R _C , R _COOL , n) (1.26−f (I)) I + T _W (5) Therefore, the equation (5) can be obtained without using the measured value of the generated voltage V.
Can calculate the maximum temperature T _MAX of the unit cell. Also,
If the battery cooling water is used at a constant temperature, the maximum temperature T of the unit cell can be obtained without using the measured value of the battery cooling water temperature.
_MAX can be calculated, the scattered electrolytic mass is calculated, the replenishment time is known, and the replenishment can be performed appropriately. <Embodiment 2> In the operation method of the present embodiment, the amount of generated power and the temperature of the battery cooling water are measured every Δt time, the maximum temperature _TMAX of the unit cell is calculated from these measured values, and The amount of phosphoric acid scattered in the matrix is calculated to determine the time of phosphoric acid replenishment, and the operation is performed by replenishing phosphoric acid based on this.

As described above, the amount of generated DC power is measured, and the measured value of the amount of generated DC power per unit cell during the operation time t [h] is A (t) [kWh]. The average DC generated power P (t) [kW] in the operating time 0 to t per is represented by the following equation (6). On the other hand, if the IV characteristic of the unit cell, V = f (I), is used, P (t)
[KW] is expressed by the following equation (7).

[0021]

P (t) = A (t) / t (6) P (t) = Iff (I) (7) That is, if the amount of DC power generation A (t) is measured, two equations are obtained. Thus, the output current I is calculated. Using the calculated value of the output current I and the measured value of the battery cooling water temperature,
As described above, the maximum temperature T _{MAX of the} unit cell is known from Expression (5), and the scattering speed w (T _MAX ) of the electrolyte at the temperature T _MAX is calculated from Expression (2). Further, by multiplying the obtained scattering speed w (T _MAX ) by the time interval of measurement, the amount of the scattered electrolyte is calculated. Therefore, the measurement is performed at predetermined time intervals, the scattered electrolytic mass is calculated, and the cumulative value of the scattered amount is calculated by sequentially adding the scattered electrolytic mass. When this value exceeds the upper limit of the scattered amount as shown in FIG. Replenish the phosphoric acid.

In the above description, the DC power generation amount A (t)
However, when measuring the AC power generation amount, the DC generation power amount can be obtained by multiplying by one stationary number, so that the amount of the scattered electrolytic mass can be calculated in the same manner, and the phosphoric acid of the electrolyte can be properly calculated. Can be replenished.
In this embodiment, the amount of generated power and the temperature of the battery cooling water are measured at every Δt time, and the maximum temperature T _{MAX of} the unit cell and the amount of the phosphoric acid scattered in the unit cell are calculated to determine the replenishment time of the phosphoric acid. Knowing this, it is decided to operate with replenishing phosphoric acid based on this, but as is often used, if the battery cooling water is kept at a constant temperature and operated, the measured value of the battery cooling water temperature will be Since the maximum temperature T _{MAK of the} unit cell can be calculated without using it, by measuring the amount of generated power at every Δt time, the amount of scattered electrolyte is known, and the phosphoric acid of the electrolyte can be effectively replenished.

[0023]

As described above, according to the present invention, a unit cell formed by arranging a fuel electrode and an air electrode on both surfaces of a matrix holding phosphoric acid as an electrolyte can be used as a cooling plate having a cooling pipe. The fuel cell is a phosphoric acid fuel cell that obtains electric energy by an electrochemical reaction by supplying fuel gas to the fuel electrode and oxidizing gas to the air electrode by passing the cell cooling water through the cooling pipe and supplying the fuel gas to the air electrode. In (1) the output current and the power generation time, or the output voltage and / or the battery cooling water, the output current and the power generation time are measured, and the electrolyte supply time is calculated from these measured values. And decided to drive.
The timing of replenishing the phosphoric acid held in the unit cell is accurately detected, and an operation method capable of stably operating the phosphoric acid type fuel cell is obtained.

(2) Also, the amount of generated power and the time of power generation, or the amount of generated power, the time of power generation, and the temperature of the battery cooling water are measured, and the replenishment time of the electrolyte is calculated from these measured values. Similarly, the time of replenishment of the phosphoric acid held in the unit cell is accurately detected, so that it is suitable as an operation method capable of stably operating the phosphoric acid type fuel cell.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a fuel cell stack operated by applying a method of operating a fuel cell according to a first embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between the amount of scattered electrolyte held in a matrix and a power generation time.

FIG. 3 is a cross-sectional view schematically showing a configuration of a unit cell which is a basic structural unit of a fuel cell stack of a phosphoric acid type fuel cell.

FIG. 4 is a cross-sectional view of a main part of a fuel cell stack configured using the unit cells having the configuration of FIG. 3;

FIG. 5 is a characteristic diagram showing the temperature dependence of the scattering speed of the electrolyte held in the matrix.

[Explanation of symbols]

 Reference Signs List 1 matrix 6 fuel electrode 7 air electrode 10 fuel cell stack 11 unit cell 12 separator 13 cooling plate 15 voltmeter 16 ammeter 17 thermometer 20 unit block

Claims (2)

[Claims] 1. A unit cell formed by arranging a fuel electrode and an air electrode on both surfaces of a matrix layer holding phosphoric acid as an electrolyte is laminated by appropriately inserting a cooling plate provided with a cooling pipe, and cooling the unit cell. Output current and power generation time, or power supply time in a phosphoric acid fuel cell in which electric power is supplied by electrochemical reaction by supplying fuel gas to the fuel electrode and oxidizing gas to the air electrode by flowing cell cooling water through the piping Measuring at least one of the output voltage and the battery cooling water temperature, the output current and the power generation time, calculating the electrolyte replenishment time from these measured values, replenishing the electrolyte and operating. How to operate a phosphoric acid fuel cell. 2. A unit cell formed by arranging a fuel electrode and an air electrode on both sides of a matrix layer holding phosphoric acid as an electrolyte is laminated by appropriately inserting a cooling plate provided with a cooling pipe, and cooling the unit cell. In a phosphoric acid type fuel cell, in which the cell cooling water flows through the pipe, the fuel gas is supplied to the fuel electrode, and the oxidizing gas is supplied to the air electrode, and the electric energy is obtained by an electrochemical reaction, Alternatively, a method of operating a phosphoric acid type fuel cell, comprising measuring an amount of generated power, a power generation time, and a battery cooling water temperature, calculating an electrolyte replenishment time from the measured values, and replenishing the electrolyte for operation.